Eohippus is an extinct genus of small equid ungulates. The only species is E. angustidens, which was long considered a species of Hyracotherium. Its remains have been identified in North America and date to the Early Eocene (Ypresian) stage.
Temporal range: Ypresian
|Reproduction of a painting c. 1920|
In 1876, Othniel C. Marsh described a skeleton as Eohippus validus, from the Greek ἠώς (eōs, "dawn") and ἵππος (hippos, "horse"), meaning "dawn horse". Its similarities with fossils described by Richard Owen were formally pointed out in a 1932 paper by Sir Clive Forster Cooper. E. validus was moved to the genus Hyracotherium, which had priority as the name for the genus, with Eohippus becoming a junior synonym of that genus. Hyracotherium was recently found to be a paraphyletic group of species, and the genus now includes only H. leporinum. E. validus was found to be identical to an earlier-named species, Hyracotherium angustidens (Cope, 1875), and the resulting binomial is thus Eohippus angustidens.
Common misconception on sizeEdit
In most early books about mammal evolution,[which?] Eohippus is described as being "the size of a small Fox Terrier",[ambiguous] even though in real life Eohippus was probably the size of a larger dog breed such as a Labrador retriever. This arcane analogy was so curious that Stephen Jay Gould wrote an essay about it in which he concluded that Henry Fairfield Osborn had described it that way in a widely distributed pamphlet. The reasons for this comparison are unclear, but Gould proposes that Osborn, a keen fox hunter, could have made a natural association between horses and the dogs that accompany them.
- MacFadden, B. J. (March 18, 2005). "Fossil Horses--Evidence for Evolution". Science. 307 (5716): 1728–1730. doi:10.1126/science.1105458. PMID 15774746.
- Froehlich, D. J. (2002). "Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)". Zoological Journal of the Linnean Society. 134 (2): 141–256. doi:10.1046/j.1096-3642.2002.00005.x.
- Gould, S.J. (1991). "Essay 10: The case of the creeping fox terrier clone". Bully for Brontosaurus: Reflections in Natural History. W.W. Norton & Co.